Means for launching, towing and recovering an oceanographic towed body in a seaway

ABSTRACT

A cable wound around a winch on a vessel has an acoustic towed body attached to the free end of the cable which also passes over a sheave mounted outward of the vessel; a saddle assembly is pivoted on the sheave, the assembly supporting the acoustic body and lifting it out of the water for storage; inward of the winch is a cable-tensioning device which consists of another sheave carried on a pivotable arm which is moved towards and away from the winch by a piston and cylinder connected to an accumulator which maintains constant pressure on the arm and thereby moves it in response to the increase and decrease in the tension of the cable when the acoustic body is towed.

United States Patent MEANS FOR LAUNCHING, TOWING AND RECOVERING AN OCEANOGRAPHIC TOWED BODY IN A SEAWAY 8 Claims, 4 Drawing Figs.

US. Cl. 114/235 R Int. Cl. B63b 21/00 Field of Search 114/235, 235.2, 235.2 F, 210

Primary ExaminerTrygve M. Blix Attorney-Douglas S. Johnson ABSTRACT: A cable wound around a winch on a vessel has an acoustic towed body attached to the free end of the cable which also passes over a sheave mounted outward of the vessel; a saddle assembly is pivoted on the sheave, the assembly supporting the acoustic body and lifting it out of the water for storage; inward of the winch is a cable-tensioning device which consists of another sheave carried on a pivotable arm which is moved towards and away from the winch by a piston and cylinder connected to an accumulator which maintains constant pressure on the arm and thereby moves it in response to the increase and decrease in the tension of the cable when the acoustic body is towed.

PATENTED SEPI 4 I87! SHEET 1 [IF 2 PATENIED SEPMISYI 3504- sum 2 OF 2 MEANS FOR LAUNCHING. TOWING AND RECOVERING AN OCEANOGRAPHIC TOWIED BODY IN A SEAWAY FIELD OF THE INVENTION This invention relates to the launching, towing and recovering of a body being towed behind a vessel.

DESCRIPTION OF THE PRIOR ART Scientific exploration and defence activities in the underwater environment has led to the increasing use of the hydrodynamic towed body as a carrying vehicle for various apparatus. In many cases the apparatus is of an acoustic nature, and thus the towed body is designed to have acoustic transparency. A prerequisite of acoustic transparency in a towed body is that it requires a thin shell and demands that the body be handled in a manner that will prevent damage to its fragile areas.

Various handling gears have been designed for towed sonar applications and these are in use with various navies. In general, the design of these hoists has involved substantial structural changes to the ship in order to install them thereon.

All existing naval handling gears for towed bodies presently known to us are complexed in nature, having one or more hydraulic winches in addition to other hydraulic actuators for controlling towing booms, etc. The resulting interrelationship between the various hydraulic components, particularly during launching and recovery procedures, becomes critical and has led to the development of highly sophisticated hydraulic control circuitry with the result that specialized personnel are required to maintain the equipment in good order.

During the development of handling gears over the years, it became apparent that a requirement existed for some form of cable tension stabilizer in order to prevent loss of the body through intermittent slackness and shock loads developing in rough waters. One such system has been designed to include a cable tension stabilizer, but due to the particular characteristics of this system, the stabilizer had to be disengaged during recovery sequences. It is, however, particularly at this time, that a cable tension stabilizer is required, since the greatest danger occurs when the ship is travelling relatively slowly and the cable length is relatively short.

A further difficulty that has been apparent in towing systems is that of controlling the position of the towing cable during ships turns at which time horizontal forces are applied to the cable and the danger of escapement of the cable from the towing sheave develops.

The primary objective of our invention is to provide a means for launching, towing and recovering a towed body entirely by the use of a single hydraulic actuator, thus achieving the ultimate in simplicity from a maintenance point of view.

A second important objective is to provide a system that can be completely self-contained within its own framework and simply mounted on the deck of a vessel without the need for structural modifications thereto.

A third important objective is to provide a cable tension stabilizer that is capable of remaining operative through the recovery sequence and until the body is safely stowed clear of the water.

A fourth important objective is to provide a simple mechanism that combines a transfer vehicle for the body between its stowage and launching position with that of a stowage cradle and positive means to prevent escapement of the cable from the towing sheave.

Other objectives will become apparent in the following disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS In describing our invention, reference will be made to the following figures in which:

FIG. 1 is a side elevation of the towed body handling gear;

FIG. 2 is an end elevation of the outboard end of the handling gear;

FIG. 3 is an end elevation of the inboard end of the handling gear illustrating the cable tension stabilizer configuration;

FIG. 4 is a fragmented side elevation showing the outboard end of the handling gear during high-speed towing.

DESCRIPTION OF THE PREFERRED EMBODIMENT Identical numerals on our several figures indicate similar parts thereon.

DESCRIPTION OF MECHANISM General Our towing system, as shown in FIG. 1, comprises a frame I mounted on the deck of a vessel 2, a winch mechanism 3, a launch and recovery mechanism 4 situated at the outboard end of said frame, and a constant tension mechanism 5 situated at the inboard end of said frame. A towed body 6 is connected to winch 3 via a tow cable 7 which passes through the transfer mechanism 4 and the shock absorber mechanism 5 in its route from the body to the winch.

Winch The winch 3, which is shown in FIGS. 1 and 2, comprises a winch drum 8 supported between trunnion bearings 9. A drive means 10, which may comprise a hydraulic or electrical gearhead motor with automatic brake, provides power to a drive shaft 1 1 fitted with a drive sprocket 12. A large sprocket 13 is attached to the sidewall of winch drum 8 and a roller chain 14 couples the winch drum to the drive means via said sprockets. Conventional control means (not shown) provide reversible drive control to the winch.

Body Transfer Mechanism The transfer mechanism 4, as shown in FIGS. 1 and 2, comprises a freely rotatable towing sheave 15 and a saddle assembly 16 mounted on a common cross-shaft 17. The saddle assembly 16 is pivotally mounted on said shaft and is spring biased by means of tension springs 18, connected between lugs 19 on the pivotal assembly and a second cross-shaft 20 on frame 1. Springs 18 are selected to have sufficient strength to lift the saddle assembly to a midpoint between its extremities of motion, but with insufficient strength to cause lift to the saddle when said saddle is carrying the body 6.

The saddle is fitted with a pair of contoured rollers 21 which are freely rotatable on shafts 22. A roller 23 is located between saddle frame members 24 such that a line vertical tangential to it may be also tangential to the groove circumference of sheave 15 when the saddle is in its lowest position.

Constant Tension Device The constant tension device,-FIGS. l and 3, comprises a sheave 25 mounted for free rotation and lateral motion on a shaft 26, which in turn is supported between a pair of arms 27. Said arms are rigidly attached to a cross-shaft 28 which is mounted on trunnions 29 situated at the inboard end of frame 1. A pair of hydraulic cylinders 30 connect a midpoint on arms 27 to rigid lugs 31 on frame 1. A gas/oil accumulator 32 connects to the head end of cylinder 30 by means of line 33. Means to adjust the gas pressure would be provided such that the cylinders may counterbalance the force generated on arms 27 by cable tension.

Operation General There are essentially three modes of operation, namely the launching operation, the towing operation and the recovery operation. These will be described individually as follows.

Launching Operation The launching operation commences with the towed body 6 in its stowed position as represented by position 34 on FIG. 1. At this time the cable tension stabilizer 5 is bottomed-out such that sheave 25 is in position 35. The body 6 is held in contact with saddle rollers 21 by cable tension generated at winch 3 and maintained by the automatic brake incorporated in drive means 10.

The launching process commences when the operator pays cable out form winch 3. The body 6 and saddle assembly 4 pivot in unison about the fulcrum at shaft 17 until the body reaches position 36 largely submerged below the waterline as shown in FIG. 1.

As additional cable is paid out the cable tension stabilizer sheave 25 will swing on its arms 27 until the cable tension is reduced sufficiently to just balance the submerged weight of body 6. When this tension is reached, continued paying out of cable will cause the body to lower away from saddle rollers 21 and commence to tow freely on the end of cable 7.

Towing Operation As the body depth increases and as the ships speed also increases, the angle at which the cable pierces the water interface will depart from a right angle, as shown in FIG. 4. Now due to the influence of springs 18, the saddle assembly 4 will swing upward such that roller 23 will remain in contact with the cable. It will be obvious that due to this action the cable can never escape the confines of the saddle. This is a most important feature since during ships turns the cable will be forced to port or starboard in addition to its trailing attitude and means must be provided to prevent the cable from riding out of the towing sheave 15. Clearly, the spring-loading device achieves this requirement. Profiled plates 37 limit the sideways bending of the cable and distribute the load rather than allow a concentrated load to occur on rollers 21.

Cable Tension Stabilizer During towing operations in a seaway, the undulations of the ship tend to induce variable cable tension. In extreme cases there is the danger of the cable going slack followed by a snapping action which imperils the cable and body. This danger is alleviated by our cable tension stabilizer. The action of the stabilizer is as follows.

When the ship is rising on a wave, the tendency for an increase in cable tension is offset by the retraction of cylinders 30 since these cylinders are supplied by a substantially constant pressure source from accumulator 32. Similarly, as the ship enters a wave trough, resulting cable slackness is prevented by extension of cylinders 30. In other words, a substantially constant pressure source of oil passes back and forth between cylinders 30 and accumulators 32 to maintain the body at a constant depth as the ship undulates.

in practice, since the gas space in the accumulator 32 is not infinitely large, the pressure rises as oil is forced into the accumulator and pressure falls as oil is driven back into the cylinders 30. However, by carefully selecting the attachment points for the linkage formed by cylinders 30, the mechanical advantage of the cylinder force about the fulcrum 28 of arms 27 will vary with the attitude of the said arms such that the mechanical advantage will be less as the gas pressure rises and vice versa. Thus the torque generated by cylinders 30 about fulcrum 28 will remain constant and constant cable tension will be maintained.

It is common practice to groove the winch drum for a single layer of faired tow cable and thus the lie of the turns is controlled by the winch drum configuration and no spooling device is required. Due to the close proximity of sheave 25 to the winch drum it is necessary that said sheave be relatively closely aligned with the cable position as it enters or leaves the winch. This is simply achieved by providing free lateral movement of sheave 25 on sheave 26 as shown in FIG. 3 so that as sheave 25 rotates it will also respond laterally as soon as misalignment of the cable starts to occur.

Recovery Operation The recovery operation commences with the hauling in of cable. As the body 6 approaches the surface, saddle 4 remains in correct register with the cable since it is spring biased against said cable and roller 23 remains in contact with said cable. Thus, when the body reaches the surface, it is immediately below the saddle.

Once contact is made between body 6 and saddle rollers 21, the cable tension stabilizer 5 will bottom-out" and cable tension will build up. When the cable tension is sufficient to overcome the weight of body 6, the body and saddle 4 will rotate in unison about shaft 17 until the body reaches position 34 and saddle 4 rests tight against suitable sto s.

-It is important to note that at t e moment of impact between body 6 and saddle 4, the energy of the impact is dissipated by the cable tension stabilizer over a period of several seconds.

The invention discussed herein has been described substantially in terms of components used. We do not, however, wish the said invention to be restricted to the precise arrangement of parts described since this disclosure is intended to explain a workable construction illustrating the concept, and is not for the purpose of limiting the invention to any subsequent embodiment or details thereof.

We claim:

1. Apparatus for launching, towing and recovering behind a vessel a body secured to a cable, comprising drivable rotary means on said vessel, said cable being wound on said drivable rotary mans, and launching means comprising first sheaved means outward of said drivable rotary means with respect to said vessel, said cable passing over said first sheaved means; and saddle assembly means mounted and pivoted about said first sheaved means and coaxial therewith, to support said body above the submersion level; means for moving said saddle assembly from a first position to a second substantially inverted position around its axis, and stop means defining the limit of pivoting motion of said saddle assembly at said second position.

2. Apparatus according to claim 7, wherein said saddle assembly means comprises spaced-apart frames, one to each side of said first sheaved means, a saddle roller to each frame. each roller being positioned in a plane substantially parallel to said first sheaved means, said cable passing between said rollers, and said body being adapted to be held against said rollers during launching and recovery sequences.

3. Apparatus according to claim 1, having spring means for swinging said saddle assembly means upwards with respect to said first sheaved means when said body is submerged.

4. Apparatus according to claim 2, having second sheaved means adjacent to and above said rollers, said cable passing over said second sheaved means.

5. Apparatus according to claim 1, having rotary means on said vessel spaced apart from said drivable rotary means, said cable being wound on said rotary means, and means moving said rotary means towards and away from said drivable rotary means in response to the increase and decrease respectively in the tension of said cable when towed.

6. Apparatus according to claim 5, wherein said rotary means is mounted for lateral movement on a shaft.

7. Apparatus according to claim 5, wherein said means moving said rotary means comprises a cylinder, a cooperating piston, the free end of which is secured to said rotary means, and an accumulator connected to said piston, the arrangement being such that a substantially constant pressure of fluid passes back and forth between said cylinder and said accumulator to maintain said body at a constant depth. I 8. Apparatus according to claim 6, wherein said shaft is secured to the free end of an arm, the other end of which is pivotably secured about a fulcrum located on said vessel, the free end of said piston being secured to said arm so that the mechanical advantage about said fulcrum will be less as the pressure rises in said cylinder. 

1. Apparatus for launching, towing and recovering behind a vessel a body secured to a cable, comprising drivable rotary means on said vessel, said cable being wound on said drivable rotary mans, and launching means comprising first sheaved means outward of said drivable rotary means with respect to said vessel, said cable passing over said first sheaved means; and saddle assembly means mounted and pivoted about said first sheaved means and coaxial therewith, to support said body above the submersion level; means for moving said saddle assembly from a first position to a second substantially inverted position around its axis, and stop means defining the limit of pivoting motion of said saddle assembly at said second position.
 2. Apparatus according to claim 7, wherein said saddle assembly means comprises spaced-apart frames, one to each side of said first sheaved means, a saddle roller to each frame, each roller being positioned in a plane substantially parallel to said first sheaved means, said cable passing between said rollers, and said body being adapted to be held against said rollers during launching and recovery sequences.
 3. Apparatus according to claim 1, having spring means for swinging said saddle assembly means upwards with respect to said first sheaved means when said body is submerged.
 4. Apparatus according to claim 2, having second sheaved means adjacent to and above said rollers, said cable passing over said second sheaved means.
 5. Apparatus according to claim 1, having rotary means on said vessel spaced apart from said drivable rotary means, said cable being wound on said rotary means, and means moving said rotary means towards and away from said drivable rotary means in response to the increase and decrease respectively in the tension of said cable when towed.
 6. Apparatus according to claim 5, wherein said rotary means is mounted for lateral movement on a shaft.
 7. Apparatus according to claim 5, wherein said means moving said rotary means comprises a cylinder, a cooperating piston, the free end of which is secured to said rotary means, and an accumulator connected to said piston, the arrangement being such that a substantially constant pressure of fluid passes back and forth between said cylinder and said accumulator to maintain said body at a constant depth.
 8. Apparatus according to claim 6, wherein said shaft is secured to the free end of an arm, the other end of which is pivoTably secured about a fulcrum located on said vessel, the free end of said piston being secured to said arm so that the mechanical advantage about said fulcrum will be less as the pressure rises in said cylinder. 